William marshall



(Nd Model.)

W. MARSHALL.

DUPLEX TELEPHONY.

Patented Sept. 26, 1893 UNITED STATES PATENT OFFICE.

WILLIAM MARSHALL, OF NEW YORK, N. Y.

DUPLEX TELEPHONY.

SPECIFICATION forming part of Letters Patent No. 505,628, datedSeptember 26, 1893.

Application filed February 28, 1892. Renewed July 8, 1892. Serial No.439,418. (No model.)

To all whom it may concern.-

Be itknown that-1,.W1LLIAM MARSHALL, a citizen of the United States,residing at New York,in the county of New York and State of New York,have invented certain new and useful Improvements in Duplex Telephony;and I do hereby declare the following to be a full, clear, and exactdescription of the invention, such as will enable others skilled in theart to which it appertains to make and use the same.

The object of my invention is to provide a system of intercommunicationby electricity in which articulate speech or telegraphic messages may betransmitted by a direct current, simultaneously with the transmission ofspeech, over the same wire by means of an induced current, the two kindsof transmission being independent of each other, and not interferingwith each other.

My invention is illustrated in the accompanying drawings, in WhichFigure 1 represents a line equipped with instruments necessary forcarrying out my invention, with terminal and intermediate stations; Fig.2 represents a similar line equipped with slightly differentinstruments; and Fig. 3 illustrates theconnections at the intermediatestations.

Referring to Fig. 1, A A are two terminal stations of a line designed tocarry telephonic communications; and A A are two intermediate stationson the same line. At the terminal station A is a battery B one pole ofwhich is grounded. The other pole is connected to line through areceiver R, and a transmitter T. The line is branched before reachingthe receiver, and one branch is wound around the core of the receiver inone direction, and the other branch is oppositely wound around the samecore. Beyond the receiver one branch passes through a resistance coil orbox r while the other is connected with the terminals of a condenser C.The two branches unite beyond the condenser on the one side, and theresistance box on the other. The transmitter T is an ordinary carbontransmitter, but the line is connected directly to its terminals, theusual induction coil being dispensed with. In this way the terminalstation instruments operate by means of a direct or primary current. Theinstruments at the other terminal station, A, are identical with thosejust described, and it is evident that operators at these two stationscan communicate with each other in the ordinary way by means of theirtransmitters and receivers. In other words, the operation of thetransmitter T, say at the station A, will affect the coil of thereceiver R at the station A, or that part of the coil which is connectedthrough the resistance box r. The other part of the coil which isconnected through the condenser C will be practically cut out and willremain unaffected by the direct current on line. At the intermediatestation A I employ a transmitter T, connected to earth, and a receiver Rwhich instruments are respectively similar to the transmitter andreceiver described in detail in my patent of September 21, 1886, No.349,312. The receiver is a condenser receiver with alternate layers oftin foil and some thin insulating material, such as paper. Every othersheet of tin foil is connected to the same pole or terminal of thereceiver, while the remaining sheets of tin foil are connected to theopposite pole. This instrument makes an excellent receiver which inpractice is equal to the best. It also serves in place of a condenserwhich by its alternate changes of static condition when the transmitterT is operated, will affect the receiver at A without disturbing orcommunicating with either of the terminal stations.

The connections at the terminal stations are illustrated in Fig. 3. Itwill be seen that the transmitter has two secondaries one of which isjoined to line and to one pole of the condenser receiver and the otherof which is joined to ground and the other pole of the receiver. Theprinciple upon which this system operates is, that the direct currentflows at the terminal stations through the branch containing theresistance and thus operates thereceiver while the induced current flowsequally through bothbranches without affecting the receiver.

In Fig. 2 the direct current circuit is equipped with the sameinstruments as are shown in Fig. 1. Theinduced current circuit at theintermediate stations is equipped with magneto receivers of theBelltype. At 0 is represented a double coil having twowires wound around amagnetic core with their oppositeendsfree. Thewiresareconnected, one tothe main line and the other to the magneto receiver and through thetelephone transmitterto ground. In other Words, the instrument C is adouble coil which is open at opposite ends and formsa sort of condenserin the circuit. The transmitter '1" may be of any of the well knowntypes.

I prefer the instrument (J (especially when Morse signals are being sentin the direct current circuit) to the condensers which are ordinarilyemployed. With the condenser, the telephone is liable to repeat thesignals at the sending station, owing to the charge and discharge of thecondenser in the induced current circuit. But when the coil 0' is used,there is no interference whatever.

I have shown in both figures of the drawings telephonic apparatus at theterminal stations, but it should be understood that I may use anyapparatus at those stations capable of being actuated by a directcurrent. The number of the stations may be increased according tocircumstances.

Having now described my invention, I claim 1. In a system of electricaltransmission, a receiving telephone having two helices oppositely wound,the two helices being in separate branches of the main circuit and oneof the said branches containing a condenser, as and for the purpose setforth.

2. In a system of electrical transmission a receiving telephone havingtwo helices oppositely wound, the two helices being in separate branchesof the main circuit, and one of the said branches containing a condenserand the other an artificial resistance, as and for the purpose setforth.

3. In a system of electrical transmission, a series of stations two ormore of which are provided with ordinary transmitting telephones withoutinduction coils, and with differentially wound receivers one winding ofwhich contains a condenser and the other an artificial resistance; andother two or more of which stations are each provided with a transmitterand a receiver and a condenser, the last two of which may or may not bethe same apparatus, as and for the purpose set forth.

4.. In a system of electrical transmission, a series of stations, two ormore of which are provided with ordinary transmitting telephones withoutinduction coils, and with differentially wound receivers, one winding ofeach containing a condenser and the other an artificial resistance; andthe other two or more of which stations are each provided with atransmitter and a receiver and a double open coil wound around amagnetic core, as set forth.

' In testimony whereof I have signed my name, in the presence of twowitnesses, this 26th day of February, A. D. 1891.

WILLIAM MARSHALL.

Witnesses:

J AMEs GREGORY, JOHN E. Ross.

